There has conventionally been known a pulse charging system for charging a secondary battery for a short period of time with an application of a pulsed constant current (see, for example, Patent Document 1). Such pulse charging system is so designed as to reduce the charging time for a secondary battery by charging the secondary battery at a charging voltage above a full charge voltage and with a large current in a short period of time during which the pulsed current flows.
There has been also known a multi-stage constant current charging system that gradually reduces the level of a charging current for constant current charge with multiple stages (see, for example, Patent Document 2). This multi-stage constant current charging system requires less charging current in the last charging state and is capable of preventing the rise of a battery temperature, which, in turn, prevents the degradation of a secondary battery.
In the pulse charging system described above, however, a terminal voltage of the secondary battery exceeds the full charge voltage as soon as a charging pulse is applied to the nearly fully charged secondary battery, degrading the secondary battery.
In the multi-stage constant current charging system, on the other hand, unlike the pulse charging system, a voltage exceeding the full charge voltage is not applied intentionally to the secondary battery, thus preventing the degradation of the secondary battery more effectively than the pulse charging system. However, the charging time is longer in the multi-stage constant current charging system than the pulse charging system.